The general aim of this project has been to study excitable membrane characteristics by a variety of physical methods. One aspect has been to improve electrical measurements of excitable membrane characteristics consistent with physical and chemical methods for the study of nerve and muscle membrane ionic channels. Two major approaches are used. The first involves the development of methods for analysis of ionic channel admittances and/or conductances by means of voltage clamp techniques. Programs for carrying out this analysis are developed. Voltage and current clamp experiments are employed to characterize the ionic currents underlying excitability in squid giant axons and chick embryonic heart cells. The contributions of the various currents to voltage oscillations, pacemaker potentials and action potentials are determined by computer simulations based on the voltage clamp measurements.